Although a variety of compact light sources are available, those with improved energy efficiency (lamp efficacy) are generally accompanied by proportionally higher manufacturing costs, and therefore by higher purchase prices that often outweigh their perceived benefit to ordinary consumers. For example, U.S. Pat. No. 4,524,302 (Berlec; 1985) discloses a general service incandescent lamp with improved efficiency having an outer envelope and an inner envelope. The inner envelope comprises what is generally known as a halogen lamp: a filament tube of quartz or high temperature glass, hermetically sealed around an incandescent filament, and filled with a relatively high pressure fill-gas including a halogen gas. Among the objects of this invention are to provide a relatively inexpensive general service incandescent lamp, to improve the arc-out resistance of the filament, and to operate at a low voltage so as to extend the life of the lamp while maintaining its wattage and even increasing its efficacy. The reduced voltages relative to a typical 120 volt AC source may be developed, for example, by an electrical transformer.
It is known that low voltage incandescent filaments are more rugged than higher voltage filaments having the same wattage, especially for coiled-wire filaments, because for any given wattage, as the design voltage is decreased the length of wire in the filament decreases, and the diameter of the wire in the filament increases. Two patents exemplify incandescent lamp designs that take advantage of this fact by providing multiple filament tubes that are series-connected within an outer envelope. This reduces the voltage drop across each filament tube without requiring a transformer, however the cost of the inner light source is multiplied by the number of filament tubes provided. U.S. Pat. No. 4,498,124 (Mayer et al.; 1985) discloses a dual halogen bulb rectangular lamp assembly with the two halogen bulbs electrically connected in series for simultaneous bulb energization. The use of two 12-volt halogen bulbs in a 24 volt reflector lamp significantly reduces the possibility of bulb burn-out because the filaments required in 12-volt halogen bulb units are made from shorter, thicker wire that can be coiled much more loosely than the filaments required in 24-volt halogen bulb units. PCT publication WO98/14733 (Katougi et al.; 1998) discloses a light bulb with a plurality of baseless small bulbs series-connected within a globe envelope, for improved earthquake resistance. FIG. 8, for example, shows two double ended filament tubes with wire loop outer leads hanging in parallel arrangement on opposite sides of a central support post.
Another factor that adds to the cost of lamps that incorporate filament tubes (e.g., halogen lamps) is the desire to protect consumers from possible non-passive failure of the filament tube. When an incandescent filament fails at end of life, an electric arc may form between broken ends of the filament. Once started, an arc has very low electrical resistance and will draw as much current as the power supply allows. In arc lamps, the power supply includes some form of ballast to limit the current to a desired amount. Incandescent power supplies do not generally provide much ballasting effect, and rely instead on fuses and/or lamp construction to quench an end-of-life arc before it can produce violent failures that may, for example, rupture the filament-containing envelope(s)—i.e., to “explode”. For filament tubes there is a small possibility of non-passive failure due to an arc that overheats the filament tube before the arc can be quenched by a fuse. A common solution is to make the outer lamp envelope out of a thick glass expected to contain a potentially rupturing inner envelope. For example, U.S. Pat. No. 6,133,676 (Chen; 2000) discloses a double enveloped halogen bulb wherein the outer glass envelope has a thickness ranging between 2 mm and 8 mm that is intended to protect a person or an animal contiguous to the bulb from a bodily injury in the event that the tubular halogen bulb explodes. Chen's FIG. 6 shows an embodiment of his outer envelope that is shaped somewhat like a common household light bulb. Obviously, the heavy glass envelope is much more expensive than a standard bulb.
Another solution for containing rupturing filament tubes is taught by related arc lamp art. For lamps that incorporate arc tubes as the light source (e.g., high intensity discharge lamps), non-passive failure is even more of a concern, particularly when the light sources are intended for household use and/or wherever they will not be contained in protective “closed” lighting fixtures. U.S. Pat. No. 5,446,336 (Gleixner et al.; 1995) discloses an explosion-protected high-pressure discharge lamp comprising a protective body surrounding the discharge vessel and located within an outer bulb. The protective body comprises one or two transparent concentric glass sleeves or tubes, at least one of which, preferably, is of quartz glass. The sleeves or tubes have open ends, and they radially surround the discharge vessel, with the open ends being capped by ceramic centering and holding elements which are retained on a lamp holder structure.
A solution for preventing rupturing filament tubes is disclosed by the present inventor in the November/December 2001 issue of IEEE Industry Applications Magazine (incorporated by reference herein), wherein a mockup of a 1972 experimental “Gemini lamp” is pictured and described as having “small twin tubes paralleling the central glass stem—these low-pressure, 60-V halogen capsules would not explode . . . . [The] two small 60-V capsules [are] in series . . . ” (pg. 16). The pictured mockup has empty glass capsules, and the design of a filament for the capsule is not disclosed. Likewise, the capsule's shape is indeterminate, and no lead wires or sealing foils are present.
FIGS. 2, 4, and 5 of the Berlec '302 patent illustrate some common features of filament tubes. FIG. 2 shows a typical quartz filament tube (22) with 1 mm thick walls that is double ended with an exhaust tube tip on the side of the tube. The tube ends are hermetically sealed by being pinched closed over a thin molybdenum foils (28, 32) that are micro-welded to inner (24c, 24e) and outer (30, 34) molybdenum lead wires. The inner lead wire may alternatively be tungsten, and is typically welded to the filament, however FIG. 3 illustrates a technique of using the inner lead wire (24c, 24e) as a spud that is forced into the single coiled end (24b, 24d) of the filament (24). It is known that this spudding process is difficult to automate given that a blunt wire end must be screwed into the coil in a way that expands the coil diameter. FIG. 4 illustrates a single ended filament tube (36) that is also made out of a high temperature glass other than quartz. In this case, sealing can be accomplished on the round lead wires (38, 40) without needing foils. The illustrated filament tubes (22, 36) are relatively bulky and heavy, and therefore require substantial mounting structures (16, 18, 20, 42, 44, 46, 48) within the outer envelope (12). FIG. 5 illustrates a somewhat smaller filament tube that is only suitable for very low voltage filaments that are consequently short enough to be mounted crosswise in the filament tube.
Several patents assigned to General Electric are indicative of the industry's efforts toward cost-reducing the manufacturing process for both filament tubes and arc tubes, particularly those small enough to be included in smaller lamps. U.S. Pat. No. 4,389,201 (Hansler and Fridrich; 1983), incorporated by reference herein, discloses a method of manufacturing metal halide discharge lamps (arc tubes) on a horizontal glass blowing lathe which is indexed by a turntable through angularly spaced work stations. A length of quartz tubing is formed into a lamp body having an enlarged bulbous midportion defining an arc chamber with tubular necks projecting in opposite directions. FIGS. 9 and 10 show the bulbous midportion (32) being formed by heating (132) while longitudinally gathering the quartz (120) and then blowing it out into a mold (134). Exhausting, flushing, and filling are all accomplished through the length of quartz tubing while it is captured in the lathe, thereby eliminating exhaust tube tips on the side of the arc tube. U.S. Pat. No. 4,810,932 (Ahlgren et al.; 1989), incorporated by reference herein, and other related patents adapt and enhance the '201 patented processes to disclose flush and pump flush processes yielding light sources for both incandescent and metal vapor discharge lamps, particularly tipless double ended filament tubes that are suitable for deposition of a reflective coating on their outer surfaces. FIGS. 1(a)–1(p) show the flush process implemented in a horizontal lathe. FIG. 1(d) shows the filament assembly (12) having a hook-shape section (12C) on one end and a loop extension section (12F) on the other for handling during the manufacturing process. FIG. 1(f) shows the filament assembly (12) being self-heated by the passage of electric current while flushing the surrounding tube (10) with an inert gas containing hydrogen. This step in the process removes oxygen contamination from within the confines of the light source body (10) and crystallizes the filament (12A) itself. By applying direct current to the filament positioned so that magnetic forces counter balance the force of gravity on the filament, the crystal structure of the filament may be set so that filament sag is avoided. FIG. 1(h) shows the filament tube's midportion (10A) being blown into a mold (30) for precise dimensional control. FIGS. 1(m) and 1(n) show liquid nitrogen (46) being used to condense a gas filling in the central portion (10a) while a torch (20) “shrink seals” the quartz body (10) around the foil sealing members (48, 50). The quartz shrinks without excessive heat because condensing the fill gas reduces the internal pressure of the body below atmospheric pressure. FIGS. 2(a)–2(l) and 3(a)–3(k) show the pump flush process implemented vertically for filament tubes and arc tubes, respectively. Minor differences from the horizontal flush process include straight ended lead wires handled by rods (72, 74) in an unspecified manner. Especially in the vertical process, the filament assembly (12) or electrodes (92) are held in place by first and second seal members abutting up against and respectively occupying the first and second neck portions of the tube body, such that bent edges of the foils (e.g., 12D, 12G) serve as springs to position and maintain the assembly (e.g., 12) on the central axis of the light source body. The seal members (12D, 12G, 92B, 94B) may be of the type described in U.S. Pat. No. 4,254,356 of Karikas, (further described hereinbelow). In preparation for mounting a finished filament tube or arc tube in an outer envelope, ends of the tube are removed by diamond saw cutting or scoring and snapping, thereby exposing a suitable length of the inlead wire extending beyond each end of the tube. As illustrated in FIGS. 6–10, the exposed lead wires are attached to a crossed lamp lead wire on at least one end, and where appropriate, to the base eyelet at the other end to provide a simplified mount structure.
U.S. Pat. No. 4,254,356 (Karikas; 1981), incorporated by reference herein, discloses inleads having a foil portion which is stiffened by reversely folded lateral edges, i.e., bent in opposite directions out of the medial plane. In making a discharge lamp, the electrode-inlead assembly is self-centering as a result of making the overall width of the foil portion and its reversely folded edges exceed slightly the internal diameter of the quartz tube or neck. The inlead assembly (1) comprises a one-piece molybdenum wire portion (2, 3) wherein the central portion (4) is foliated by longitudinal rolling to a thickness of about 0.0009″ at the center. Karikas further teaches that the foliated portion (4) may also be produced by cross rolling and by swaging or hammering of the original wire, or may also use a composite foil comprising a cut length of molybdenum foil to one end of which is welded a molybdenum wire and to the other end a tungsten wire. No further details are provided about the proposed hammering process, and the present inventor is not aware of any practical mass production implementations of a foliation-by-hammering process in the lamp-making industry.
It is an overall object of the present invention to significantly reduce the manufacturing cost of high-efficacy light sources, particularly those intended for household use, and more particularly those incorporating incandescent filament tubes contained within a protective outer envelope. Accordingly, it is an object to effectively eliminate the likelihood of non-passive failure for filament tubes in lamps made according to the invention. Accordingly, it is an object to mass-produce inexpensive filament tube envelopes. Accordingly, it is an object to mass-produce inexpensive foil/leadwire assemblies. Accordingly, it is an object to simplify leadwire-to-filament assembly and the handling of said assembly. Accordingly, it is an object to improve manufacturing efficiency for the flush-fill process. Accordingly, it is an object to improve the mounting of filament tubes within an outer envelope. Other subsidiary objects may become evident from the foregoing specification of the present invention.
A further object of the invention is to utilize suitable features of the inventive filament tubes in order to cost-reduce double ended arc tube lamp manufacturing.